1. Field of the Invention
The present invention relates to the field of mass spectroscopy. More particularly, the present invention relates to the field of mass spectroscopy directed to a novel system and method that enables combining ion storage and ion mobility separation on the same time scale so as to provide high duty cycle analysis of the collected ions.
2. Discussion of the Related Art
High-throughput refers to a technology in which a large number of measurements can be taken in a fairly short time period. “Ome” and “omics” are suffixes that are derived from genome (the whole collection of a person's DNA) and genomics (the study of the genome). High-throughput analysis is essential when considering data at the “omic” level, that is to say considering all DNA sequences, gene expression levels, or proteins at once. Without the ability to rapidly and accurately measure tens and hundreds of thousands of data points in a short period of time, there is no way to perform analyses at this level. In particular, high-throughput analysis in various OMICS' requires a high duty cycle of operation, often by using a configured mass spectrometer. This requires that mass analysis be done faster than ion accumulation or the ions desired to be interrogated must be stored in a manner that enables spectral quality mass analysis. With ever increasing of brightness of the ion sources, the second approach is beneficial.
To provide such ion storage with mass analysis creates a need for higher storage capabilities of the ions. Relative high capacity storage of ions in the field of mass spectroscopy presently entails configurations of linear RF multipole rod assemblies, more often quadrupole arrangements, wherein phases of an applied RF voltage are alternatively applied to opposing rod pairs. From such an arrangement, a pseudo potential is created that enables accelerating the ions in the interior of the device towards the axis so as to enable oscillations around the potential minimum along the length of the interior axis. Applied DC fields located at the ends of the rod poles or applied to predetermined sections of the rods enables trapping of desired ions. Moreover, such devices can also be provided with a buffer inert gas, e.g., Helium, Neon, Argon, to assist the ions in losing their initial kinetic energy via low energy collisions. In the right configuration, introduction of such gases also enables different ion species to be separated by their ion mobility, i.e., by ion mobility spectrometry (IMS).
The utility of ion mobility spectrometry (IMS) for separation of ions has been demonstrated extensively, but IMS combined with mass spectrometry (MS) has remained a niche technique, mainly because of the loss of sensitivity due to ion losses within the combination of techniques. IMS, in particular, remains a desired technique to be coupled with MS because of the speed of the separation technique. Specifically, IMS exploits the beneficial aspect that different particles diffuse through a gas at different speeds, depending on their collision cross-sections with the introduced gas molecules. While neutrals diffuse randomly (via Brownian motion), ions in an applied electric field drift in a defined direction with the velocity controlled by their mobility (K). Such a quantity generally varies with the field intensity E but IMS is often run in a low-field regime where K (E) is substantially constant. In that limit, K depends on the ion/buffer gas collision cross-section Ω, of which allows a spatial separation of different ions.
Accordingly, a need exists for providing higher ion storage configurations that capitalize primarily on ion mobility separation to provide high duty cycle analysis of the collected ions. The present embodiments, as disclosed herein, addresses this need by providing novel arrangements designed to confine desired high ion loads in groups after ion mobility separation and can be directed to scan out desired groups of ions to coupled analyzers while continually filling storage region(s).
Background information on an ion storage bank system is described and claimed in U.S. Pat. No. 7,718,959 B2, entitled, “STORAGE BANK FOR IONS,” issued May 18, 2010, to Frantzen et al., including the following, “[t]he invention relates to instruments for storing ions in more than one ion storage device and to the use of the storage bank thus created. The ion storage bank includes several storage cells configured as RF multipole rod systems, where the cells contain damping gas and are arranged in parallel. Each pair of pole rods is used jointly by two immediately adjacent storage cells such that the ions collected can be transported from one storage cell to the next by briefly applying DC or AC voltages to individual pairs of pole rods. The ions can thus be transported to storage cells in which they are fragmented or reactively modified, or from which they can be fed to other spectrometers. In particular, a circular arrangement of the storage cells on a virtual cylindrical surface makes it possible to accumulatively fill the storage cells with ions of specific fractions from temporally sequenced separation runs.”
Background information for a mass spectrometer system that incorporates a 2-D “traveling wave” ion guide for moving trapping regions along the ion guide, is described and claimed in, EP No. 1 505 632 A1, entitled, “MASS SPECTROMETER,” published Feb. 9, 2005, to Bateman et al., including the following, “[a] mass spectrometer is disclosed wherein ions from a pulsed ion source 10, 11 are dispersed in a drift region 16 so that the ions become separated according to their mass to charge ratios. The ions are then received by an ion guide 1 in which multiple trapping regions are created and wherein the multiple trapping regions are translated along the length of the ion guide 1. The ion guide 1 receives the ions so that all the ions trapped in a particular trapping region have substantially the same or similar mass to charge ratios. The ions are released from the exit of the ion guide 1 and the pusher/puller electrode 14 of an orthogonal acceleration Time of Flight mass analyzer is arranged to be energized in synchronization with the ions emerging from the ion guide 1; The trapping regions may be translated along the ion guide 1 with a velocity which becomes progressively slower and the delay time of the pusher/puller electrode 14 may be progressively increased.”
Another exemplary source of background material for 2D-guides using stacked plates or rings arranged parallel and generally transverse to the travel axis of ions can be found in (See Gerlich et al, (1992): Inhomogeneous Electrical Radio Frequency Fields: A versatile tool for the study of processes with slow ions. Adv. In Chem Phys LXXXII, 1. ISBN 0-471-53258-4, John Wiley and Sons). Generally, such structures are also arranged as radio frequency (RF) ion guides and operated under elevated pressures to efficiently transmit ions from one portion of a spectrometer to another. These devices work on the principle of so called “effective potential wells” that can trap the ions in these wells for extended periods of time either by the use of cylindrical geometry devices such as conventional Paul traps, or using linear geometry devices such as multipole guides or ring sets with end plates providing a trapping D. C. potential.